Desmodromic mechanism

ABSTRACT

A desmodromic mechanism having transmission elements connected to and supported by an intermediate element and a primary and a secondary cam both in permanent contact with the transmission elements. The transmission elements, the intermediate element, the primary and secondary cams are assembled to one another to compulsorily move in rotation or linearly relative to one another. The various elements are also assembled in such a way as to form sealed variable volume chambers.

BACKGROUND OF THE INVENTION

The present invention has for its object a desmodromic mechanismcomprising a primary element and a secondary element mechanicallyinterconnected by a desmodromic connection, which is to say such thatthe speed of one of said elements precisely determines a speed for theother.

Such mechanisms are found in speed changers, speed multipliers orreducers, hydraulic, pneumatic or internal combustion motors,compressors, pumps, jacks, linear actuators, etc.

To provide angular or linear drives for mechanisms whose object is totransmit movements permitting changing volumes to obtain pumps,compressors, etc., or to reduce or multiply speed with a certainprecision, there is used gearing which has in certain cases majordrawbacks, such as problems of lubrication, noise, size, difficulty toobtain movement without play, cost, etc.

The object is to provide the mechanisms mentioned above by a simple,precise and robust desmodromic system of a cost lower than that ofconventional embodiments.

This system permits the use of plastic or ceramic materials underoptimum conditions. It is possible to provide mechanisms which canoperate without lubrication and have high mechanical resistance.

By the reduction of speed between the input shaft and the intermediateelement carrying the transmitters, great improvements are enjoyed in themechanisms relying on variable volume chambers.

The object of the present invention is to provide such a desmodromicmechanism which will be inexpensive, robust, easy to produce, which hasno gearing and which permits producing linear or rotating motion of thedriven element from a rotating movement of the motor element, or viceversa.

SUMMARY OF THE INVENTION

The present invention has for its object a desmodromic mechanism tendingto overcome the mentioned drawbacks and permitting achieving thementioned objects. This desmodromic mechanism is characterized by thecombination of elements set forth in claim 1.

The accompanying drawing shows schematically and by way of exampleseveral embodiments of the mechanism of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view, partially exploded, of a first embodimentof the mechanism.

FIGS. 2 through 6 show the successive positions of the mechanism forsuccessive rotations of 90° of the primary element of the mechanism.

FIGS. 7 and 8 show an axial cross-section and a longitudinalcross-section of the mechanism in use in an internal combustion engine.

FIGS. 9 to 12 show the positions of the elements of the mechanism forthe four cycles, intake, compression, explosion and exhaust, of themotor.

FIG. 13 shows an axial cross-section of the mechanism used as acompressor.

FIGS. 14 to 18 show the successive positions of the mechanism of FIG.13, showing the operation of the latter as an air compressor.

FIGS. 19 to 23 show the successive positions of a second embodiment ofthe mechanism for angular increments of 90°, of the primary element; thesecondary element is stationary.

FIGS. 24 to 28 show the successive positions of the second embodiment ofthe mechanism, for increments of 30°, of the secondary element, theintermediate element being stationary.

FIGS. 29 and 30 show two modifications of a third embodiment of themechanism comprising five transmission members.

FIGS. 31 and 32 show a fourth embodiment of the mechanism in whichfriction is reduced by the use of rotatable elements.

FIG. 33 shows in plan view and schematically, a modification of theembodiment of the mechanism shown in FIGS. 31 and 32.

FIGS. 34 and 35 show a fifth embodiment of the mechanism.

FIG. 36 is an axial cross-section of a sixth embodiment of themechanism.

FIGS. 37 to 41 show the positions of the elements of the mechanism ofFIG. 36 for successive increments of 90°, of the primary element whenthe secondary element remains stationary.

FIG. 42 is a longitudinal cross-sectional view of a seventh embodimentof the mechanism.

FIGS. 43 to 47 show the successive positions of the mechanism of FIG. 42for angular displacements of 90°, of the secondary element, theintermediate element being stationary.

FIGS. 48, 49 and 50 are schematic views of the first embodiment of themechanism shown in FIGS. 1 to 6, showing a particular fundamentalcharacteristic of the mechanism present in all its embodiments.

FIGS. 51 and 52 are axial and longitudinal cross-sections of an eighthembodiment.

FIGS. 53 and 54 are developed views of the essential portions of themechanism shown in FIGS. 51, 52 in two different positions of themechanism.

FIGS. 55, 56 and 57 are longitudinal and axial cross-sections,respectively, of a ninth embodiment of the mechanism.

FIGS. 58 to 62 are longitudinal cross-sections and FIGS. 58A to 62A areaxial cross-sections, of a tenth embodiment of the mechanism, showingthe successive positions of the latter for increments of 45°, of theprimary element, the intermediate element being stationary.

DETAILED DESCRIPTION OF THE INVENTION

The first embodiment of the desmodromic mechanism according to theinvention, shown in FIGS. 1 to 6, comprises an input shaft 1 whose endis provided with a primary cam 2 here formed by an eccentric with atrack.

This mechanism also comprises an output shaft 3, concentric with theinput shaft 1, whose end is provided with a plate 4 comprising axialprojections 5 defining between them straight grooves or guides 6. Thisassembly constitutes an intermediate element of the mechanism.

When mounted in service position, the primary cam 2 is located in themiddle of the projections 5 of the intermediate element.

A casing 7 comprises bearings 8, 9 for the input shaft 1 and outputshaft 3 and has an internal cavity 10 in which are disposed the plate 4and the primary cam 2. The peripheral wall of this internal cavity 10 ofthe casing 7 constitutes a secondary cam comprising in this embodimenttwo tracks 11, 12.

Movement transmission members 13 are present in the form of cylindricalrollers and are disposed in each of the guides 6 located between theprojections 5 of the plate 4 of the intermediate element 3. Thesetransmission members 13 slide without play in the guides 6 between theprojections 5 and are in contact by their periphery simultaneously withthe primary cam 2 and the secondary cam with two tracks 11, 12.Moreover, these transmission members 13 are in permanent bearingrelation against at least one of the lateral surfaces of the guides 6 ofthe intermediate element. Thus, each transmission member 13 is inpermanent contact with the primary cam 2, the secondary cam and theintermediate element.

If the casing 7 is held stationary and the input shaft 1 is rotated,there is obtained the successive positioning of the elements of themechanism. From FIG. 1 to FIG. 2, the primary element 1 has undergone arotation of 90°, the track of the primary cam forces the transmissionmember 13 b outwardly, following the profile of the secondary cam, whichgives rise to the rotation, in the same direction, of the intermediatemember and the output shaft 3.

A subsequent rotation of 90° (from FIG. 3 to FIG. 4) of the input shaft1 gives rise, by the primary cam track, to the displacement outwardly ofthe transmission members 13 b and 13 c, still in contact with thesecondary cam, giving rise again to a rotation of 30° of theintermediate element. From the position of FIG. 4 to that of FIG. 5,force is transmitted from the primary cam 2 to the intermediate memberby the transmission members 13 a and 13 c. When the primary cam hasundergone a new displacement of 90°, the intermediate element hasundergone a new rotation of 30°. Then by a new rotation of 90° of theprimary cam 2 (from FIG. 5 to FIG. 6) the transmission members 13 a and13 c continue to drive the intermediate element through a new movementof 30°. At this time, the initial configuration of FIG. 2 is resumed,the transmission member 13 c having taken the position of thetransmission member 13 a. The input shaft 1 and the primary cam 2 haveundergone a rotation of 360° and having done this have drivendesmodromically the intermediate element over an angular distance of120°, namely ⅓ of the angular distance traversed by the primary element1. There is thus obtained a speed reduction of 3 to 1 between the inputshaft 1 and the output shaft, and this with a gearless mechanism havinga minimum of friction, indeed solely rolling movement. The mechanismdescribed is strictly desmodromic, which is to say that the speeds ofthe elements 1 and 3 are strictly proportional. If the speed of theinput shaft 3 is constant, the speed of rotation of the output shaft 3will also be constant, without any variation, of a value three timesless than that of the input shaft 1.

It will be seen that, when the casing is stationary, for an angularmovement of the primary cam of 360°, the intermediate element undergoesa rotation in the same direction of 120°, there is thus exactly a ratioof 1 to 3. On the contrary, if it is the intermediate element which isfixed, a rotation of 360° of the primary cam gives rise to a rotation,in the opposite direction, of the casing, of 180°; there is thus in thiscase a ratio of 1 to 2.

In such a mechanism, the demultiplication ratios are always wholenumbers.

Referring to FIG. 49, it will be seen that the transmission member 13 ais in contact with the tip of the primary cam 2 and the hollow 11 of thesecondary cam. In this position, the tangents to the points of contactof the transmission member 13 a with the primary and secondary cams,respectively, are parallel to each other. In this position, thetransmission member 13 a cannot transmit any torque or any movement.

If the same tangents are traced for the transmission members 13 b and 13c, the points of contact of these transmission members with the primaryand secondary cams are displaced and are no longer located on a diameterof the transmission member, these tangents then forming an acute angleβ, γ between them. It will be noted that these angles β, γ are locatedone in the clockwise direction and the other in the counterclockwisedirection, and hence are opposite. Thus, when the mechanism is stopped,the relative position of the three elements, the primary cam 2, thesecondary cam 11, 12 and the intermediate 5, 13, is blocked in onedirection by the transmission member 13 c and in the other direction bythe transmission member 13 b. The mechanism accordingly cannot undergoany unintended movement.

On the other hand, when the primary cam 2 is driven in rotation, in theclockwise direction, the transmission member 13 b is pressed outwardly,giving rise to a movement of the intermediate element also in theclockwise direction. This is made possible because simultaneously withthe rotation of the primary cam 2, the angle γ is progressivelyincreased, which permits a passive movement of the transmission member13 c.

Returning to FIGS. 1 to 6, it will be seen that the transmission membersare active, for a rotation of the primary cam 2 in the clockwisedirection, when they are located in the quadrants II and IV and passivewhen they are located in the quadrants I and III. Because in the courseof rotation of the intermediate element there is always at least onetransmission member located in one of the quadrants II and IV and atleast one other in one of the quadrants I and III, there willaccordingly always be at least one transmission member that is activeduring rotation of the mechanism. Upon stopping the mechanism, on theother hand, this arrangement ensures that it is blocked in the twodirections no matter what the angular position in which the intermediatemember has stopped.

It will be seen that the volume of the space 10 contained between thetwo transmission members 13, the peripheral surface of the projection 5and the intermediate element in contact with these transmission members13 and the portion of the internal peripheral surface of the casing 7,or secondary cam, is variable as a function of the rotation of the inputshaft 1 and the primary cam 2. This particularity permits designing usesfor this mechanism not only as a reducer or multiplier, but also as amotor, a compressor, or a pump.

In the case in which the projections 5 do not ensure sealing of thevolume 10, either because the projections comprise passages, or becausetheir height is less than that of the transmission members 13, variablevolume 10 is then determined by two adjacent transmission members andthe portions of the primary and secondary cams comprised between thesetwo transmission members.

It will be noted that the number of transmission members 13 is equal tothe number of tracks of the primary cam 2, increased by the number oftracks 11, 12 of the secondary cam, in this example equal to three.

It will also be noted (FIG. 2) that the distance between the high pointof the track of the primary cam 2 and the high point 11 of the secondarycam of the secondary element 7, is equal to the diameter of thetransmission member 13, namely the distance comprised between two endpoints of contact of this transmission member.

The same is true for the distance (FIG. 3) separating the low point ofthe primary cam 2 and the low point of the secondary cam.

The sum of the length y between the center of the transmission memberand its contact with the primary cam, and the length z between thecenter of the transmission member and its contact with the secondarycam, is equal for all the elements of a same mechanism and invariable inall the positions of operation (FIG. 48).

It will be noted in this arrangement that in the course of the movementof the mechanism, the center O of the three transmission members 13 ispermanently located on a circle whose center coincides with the axis Xof the primary cam 2. In this case, the primary cam 2 is constituted byan eccentric whilst the secondary cam is constituted by an oval surface.The primary cam 2 is located within the secondary cam.

The frictional or rolling forces are very much reduced, because they arelimited to the sliding of the transmission members 13 in their guides 6and to their rolling against the primary cam 2 and the secondary cam.

From the description of this first embodiment of desmodromic mechanismaccording to the invention, it will be evident that this mechanism iscomprised essentially by a primary cam, a secondary cam and anintermediate element defining linear guides in which slide the movementtransmission members; the two cams and the intermediate element aremoveable relative to each other.

For clarity and precision of the description which follows, of thedifferent embodiments of the mechanism, first to define that the primarycam can be located within the secondary cam or vice versa, and that thetwo cams can oppose axially; but always the intermediate element will belocated between the two cams.

The two cams can be movable and the intermediate element stationary orone of the cams and the intermediate element can be movable but then theother cam is stationary. One or the other of the cams can be driven, theother cam or the intermediate element being then the driver, or viceversa.

By definition, there will always be meant by the primary cam, that oneof the two cams which has the fewer tracks.

FIGS. 7 and 8 show in transverse and longitudinal cross-section, a useof the mechanism described above for implementing an internal combustionengine. For a better understanding and simplification of thedescription, the same references numerals as in FIGS. 1 to 6 will beused to indicate the corresponding members.

In this use, the casing 7 is maintained stationary and constitutes themotor block. For reasons of construction, it is made of three pieces inthis example, two plates 7 a and 7 b as well as a ring 7 c. These threepieces 7 a, 7 b and 7 c are secured to each other in stationary.

The intermediate element comprises a shaft 3 rotating in the two plates7 a, 7 b of the casing. This shaft 3 is secured to two flanges 20interconnected by bridges 21 equivalent to the projections 5 of thefirst embodiment of the mechanism. These flanges 20 turn without playand in a sealed manner relative to the ring 7 c whose intermediateportion of the internal surface constitutes the secondary cam comprisingthe two tracks 11, 12.

The input shaft 1 is rotatable in the shaft 3 and carries the primarycam 2.

The transmission members 13 are disposed between the bridges 21, theinternal surface or secondary cam of the casing 7 c, the primary cam 2and the flanges 20. These transmission members 13 ensure sealed contactbetween the pieces with which they are in contact and thus delimit threevariable volume chambers 10 a, 10 b, 10 c. To limit the friction forcesbetween the primary cam 2 and the transmission members 13, there isprovided in this embodiment a needle bearing 22 between an eccentric 23secured to the shaft 1 and a circular ring constituting the externalsurface of the primary cam 2.

The ring 7 c of the casing also comprises an inlet conduit 24 for acombustible mixture, an exhaust conduit 25 for combustion gases and aspark plug 26, angularly offset by about 120° from each other.

The transmission members 13 can be tubular and provided with sealingmeans guaranteeing good compression and a low coefficient of frictionand rolling.

The four phases of the cycle of operation of the motor are shown inFIGS. 9 to 12. FIG. 9 shows the intake of the gaseous mixture into thevariable volume chamber 10 c through the conduit 24. The primary cam 2and the intermediate element turn in a clockwise direction. FIG. 10shows the motor at the moment at which compression is at the point ofreaching the maximum in the variable volume chamber 10 c and at whichthe ignition is caused by the spark plug 26. The rotation of theelements continues, and FIG. 11 shows the motor in the expansion phaseof the variable volume chamber 10 c; then FIG. 12 shows the exhaust 25of the variable volume chamber 10 c. It is evident that the threevariable volume chambers pass through the same four-cycle operation,such that for one complete revolution of the intermediate element 3, 21each variable volume chamber 10 a, 10 b, 10 c will have an ignition andexpansion phase. This having been done, the shaft 1 and the primary cam2 will have effected three complete turns.

Such a motor therefore has two torque elements: the shaft 1 secured tothe primary cam, and the intermediate element 3, the speed of rotationof this intermediate element 3 being three times less than that of theprimary element 1.

FIGS. 13 to 18 show another embodiment of the mechanism and its use as acompressor.

The mechanism comprises a casing formed by two flanges 130, 131, ofwhich one comprises a hub 132, connected by a ring 133 whose internalsurface 134 constitutes the secondary cam which here has four tracks.

The intermediate element is formed of two flanges 135, 136 connected bybridges 137, provided with air passages 137 a, defining between themrectilinear radial guides in which slide the transmission members 138formed by tubular elements. The connection between each rotatable flange135, 136 and the fixed ring 133 is sealed.

The mechanism again comprises a primary cam 139 with a track formed byan eccentric secured to an input shaft 140 rotatable in the flange 130and the hub 132 of the casing.

The transmission members 138 sealingly slide between the flanges 135,136 but are not sealed in the radial guides and are in permanent andsealed contact with the primary cam 139 and the secondary cam 134. Thesetransmission members thus define with the primary and secondary camssealed chambers 150 of variable volume, five in number.

This mechanism also comprises at least one inlet opening 141 in the hub132 of the casing, communicating by a bore 132 in the flange 136 with adistribution sector 143 recessed in one of the side surfaces of theprimary cam 139.

This mechanism also comprises an exhaust conduit 144 in the hub 132 ofthe casing, communicating with a hole 145 provided in the end of theshaft 140 and the primary cam 139, opening toward the periphery of thisprimary cam.

The distribution sector 143 extends over an angular extent substantiallyequal to 90°, and one of its ends is diametrically opposite the axis ofthe hole 145.

In such an arrangement of the mechanism, the casing is stationary, andfor a complete revolution of 360° of the input shaft 140 secured to theprimary cam 139, the intermediate element undergoes a rotation of 72°,namely ⅕ of a turn.

The operation of the compressor thus produced by the mechanism is thefollowing, with reference to FIGS. 14 to 18. In FIG. 14, the variablevolume chamber 150 a is at its least volume, isolated from the intake143 and the exhaust 145. The variable volume chamber 150 b is connectedto the exhaust 145 whilst the variable volume chambers 150 d and e areconnected to the intake. Rotation of the input shaft 140 and of theprimary cam 139 by 45° gives rise to a rotation of the intermediateelement and of the variable volume chambers 150, of 9°, bringing themechanism into the position shown in FIG. 15.

The variable volume chamber 150 a is connected to the intake and thevariable volume chamber 150 b to the exhaust. The volume of the chamber150 a increases whilst the volume of the chamber 150 b decreases,emptying the gas which it contains into the exhaust conduit 144.

Upon further rotation by 45° of the shaft 140, the position shown inFIG. 16 is reached, wherein the chamber 150 b is at its smallest volumeand it is no longer connected to the exhaust but it is the chamber 150 cwhich is connected also to the exhaust whilst the chambers 150 d and eare connected to the intake. Upon a further rotation of the primary camby 90°, to arrive at the position shown in FIG. 17, the variable volumechamber 150 c decreases in volume and expels its contents through theexhaust. Upon a further rotation of the primary cam by 90°, to reach theposition shown in FIG. 18, the variable volume chamber 150 d expels itscontents to the exhaust whilst the chambers 150 c and 150 b refillbecause they are connected to the intake.

Due to the rotation of the input shaft 140, the exhaust is connectedsuccessively to each variable volume chamber while there volumedecreases and the chambers refill during increase of their volume. Themechanism thus constitutes a continuous compressor. The torque necessaryfor the input shaft 140 to obtain a high rate of compression is reducedby the demultiplication of 5 to 1 of the rotative movement between theinput shaft and the intermediate element which defines with thesecondary cam the variable volume chambers.

It will therefore be seen that the mechanism according to the inventioncan be used as a mechanical reducer or multiplier (FIGS. 1 to 6), as aninternal combustion engine (FIGS. 7 to 12) or as a compressor orhydraulic or pneumatic motor (FIGS. 13 to 18). It is also used to carryout linear movements for example of jacks, linear actuators of thedisplacement of elements of indefinite length by replacing racks,chains, etc. Thus, by using the same mechanical principle, several verydifferent applications can be carried out, which renders this mechanismparticularly polyvalent.

In what follows, there will be described several more embodiments andvariations of the mechanism which, although they refer to the use as aspeed reducer or multiplier, can of course be used in the conceptsmentioned above.

The embodiment of the desmodromic mechanism according to the inventionshown in FIGS. 19 to 23 comprises an input shaft 1 secured by a primarycam 2 to a track and a fixed casing 7 having a secondary cam with threetracks formed by the internal peripheral wall of the casing 7.

The intermediate element in this case comprises an output shaft securedto a plate 4 having four projections 5 uniformly spaced about itscircumference and defining between them four guides 6 receiving thetransmission members 13, sliding without play in these guides andbearing against the primary cam 2 and the secondary cam and theseprojections 5.

In this embodiment, if the casing 7 is maintained stationary andsuccessive rotations of 90° are imposed on the primary cam 2, there areobtained the successive positions illustrated in FIGS. 19 to 23. Whenthe primary cam 2 a performs one complete revolution, passing from FIG.19 to FIG. 23, the intermediate element 4, 5 has carried out a rotationof 90° as shown by the position of projection 5 a and the transmissionmember 13 a.

The sum of the tracks of the primary cam 2 and of the tracks of thesecondary cam 7 is four, equal to the number of transmission members 13.

In this example, there is a demultiplication ratio of 4:1 between theangular movements of the input shaft 1 secured to the primary cam 2 andthe intermediate element 3, 5. The two shafts 1, 3 turn in the samedirection.

In FIGS. 24 to 28, there are shown the successive positions of amechanism identical to that of FIGS. 19 to 23 but in which it is theintermediate element 4, 5 which is maintained stationary. Thus, for eachrotation of 90° of the input shaft 1 and of the primary cam 2 in thedirection of the arrow F, it will be seen that the casing 7 performs arotation in the reverse direction of 30°. Thus, for one turn of theprimary cam 2 in the clockwise direction there is obtained a rotation of120° of the casing 7 in the counterclockwise direction, the track A ofthis casing passing from its position shown in FIG. 24 (noon) to thatshown in FIG. 28 (8 a.m.).

For one complete revolution of the primary cam 2, the casing performs arotation of ⅓ of a turn in the reverse direction. There is thus carriedout a demultiplication of 3 to 1.

In the embodiment shown in FIG. 29, the input shaft 1 has an eccentric30 on which is idly mounted a tubular primary cam 31 via a needlebearing 32. This primary cam 31 has a single track.

The intermediate element, secured to the output shaft 3, comprises aplate 4 provided with five projections 5 uniformly disposed about theaxis of said plate 4 and defining five rectilinear radial guides 6 eachreceiving one transmission member 13 sliding without play in theseguides and the transmission members 13 are tubular to reduce the inertiaand deform slightly during rotation of the system and prevent play uponstopping.

The internal peripheral wall of the casing 7 has four tracks 33 whichconstitute the secondary cam.

The number of transmission members 13 is equal to the sum of the tracksof the primary cam 31 and the tracks 33 of the secondary cam, namelyfive. If the casing 7 is maintained stationary, there is obtained foreach complete revolution of the primary cam 30, 31 an angulardisplacement in the same direction of the intermediate element 4, 5 of72°, namely ⅕ of a turn.

In the modification of this third embodiment shown in FIG. 30, the shapeof the secondary cam is different although it also comprises four tracks34. The rule of the sum of the values y, z applies to these twovariations.

In these two variations also, the distance separating the low point ofthe primary cam 2 from each low point of the secondary cam is equal tothe diameter of a transmission member, as is also the distanceseparating the high point of the primary cam from each high point of thesecondary cam when these points are aligned across a diameter of themechanism.

Here again, the center of the transmission members 13 is always locatedon a circle whose center coincides with the axis of the eccentric andhence of the primary cam 30.

FIGS. 31 and 32 show an embodiment of the mechanism comprising an inputshaft 41 secured to a central drum 42 carrying at each of its axial endsa primary cam with one track 43, these cams 43 being exactly alignedangularly. This input shaft 41 rotates in an intermediate elementcomprising two flanges 44 each secured to a bearing 45, located onopposite sides of the primary cams 43. These bearings freely pivot inthe casing formed by two lateral flanges 46 interconnected by a ring 47whose central section 48 of the internal surface constitutes thesecondary cam.

The primary cam 43 is constituted by an eccentric comprising one trackand the secondary cam 48 by a casing having seven tracks uniformlydistributed about the axis of the mechanism.

This mechanism also comprises eight transmission members, eachconstituted by an axle 49 bearing a central roller 50 coacting with thesecondary cam 48 and two lateral rollers 51 coacting respectively eachwith one of the primary cams 43. The axles 49 slide without play inradial slots 52 of the flanges 44 of the intermediate element andserving as guides to the transmission members.

There will be found in this embodiment the same criteria regulating thenumber of transmission members 49, 50, 51 which is equal to the sum ofthe tracks of the primary cam 43 and the seven tracks of the secondarycam 48, namely, in this case, eight.

The same is true for the separating distances, taken on the radius ofthe mechanism, the high and low points respectively of the primary andsecondary cams are equal to the diameter of the transmission members.The axles 49 of the transmission members are disposed about acircumference whose center coincides with the axis of the eccentric 43.

In this embodiment, the intermediate element and its output shaft 45perform ⅛ of a turn when the primary cam 43 and its input shaft 41 carryout one complete revolution. There is therefore a ratio of 8 to 1. Thisembodiment permits transmitting high torque, almost all the frictionbeing avoided by the rotation of the assembly of the rollers forming thetransmission members.

FIG. 33 shows a modification of this embodiment in which one of twotransmission members 51 has been omitted. The secondary cam 48 againcomprises seven tracks, the primary cam 42 one track, but the number oftransmission members 52 is four. This does not modify thedemultiplication ratio, which again is equal to ⅛. This solution permitssimplifying the production for uses in which the cost is important andthe input torque low.

In this embodiment, the intermediate member is of the type of that shownin FIGS. 1 to 6 for example, and comprises a plate 4 provided withprojections 5 constituting the linear guides. The transmission members52 are constituted by cylindrical rollers.

In the embodiment shown in FIGS. 34 and 35, the mechanism comprises aninput shaft 61 comprising two angularly opposite eccentrics 62 formingtogether a primary cam with two tracks.

The intermediate element comprises an output shaft 63 carrying a plate64 provided with three projections 65 defining between them the radialrectilinear guides for the transmission members 66 juxtaposed two by twoin each of these guides and each coacting with one of the eccentrics 62.One of the ends of the input shaft 61 is journelled in the output shaft63 whilst the other is journelled in a half 67 of the casing 67, 68.

The casing 67, 68 has on its internal surface of each of its halves 67,68 a secondary cam 69, 70 each with two tracks. The secondary cams 69,70 are offset by 90° so as to form a secondary cam with four trackstotal.

The sum of the tracks of the primary cam 62 and of the tracks of thesecondary cam 69, 70 is six, equal to the number of transmission members66.

When the primary input shaft 61 carries out one complete turn, theoutput shaft 63 of the intermediate element performs a rotation of 120°as in the first embodiment described, the demultiplication ratio beingthree.

It will be seen from the description of the preceding embodiments and oftheir operation, that the ratio of the speeds of movement, for amechanism whose casing is fixed, is equal to the number of tracks of thesecondary cam increased by the number of tracks of the primary cam,divided by the number of tracks of the primary cam, namely (3+1):1=4 inthe example of FIGS. 19 to 23 and (7+1):1=8 in the example of FIGS. 31,32, 33 and (6+2):2=3 in the example of FIGS. 34, 35. The input andoutput shafts turn in the same direction. For a secondary cam with fourtracks=360°:4=90°; six transmission members 360°:6=60°; 90°−60°=30°;90°:30°=3; demultiplication 1:3; 60°:30°=2, demultiplication 1:2.

On the contrary, when it is the intermediate element which is maintainedfixed, a rotation of one complete turn of the casing gives rise to arotation of the primary cam or of the input shaft equal to the number oftracks of the secondary cam divided by the number of tracks of theprimary cam, namely three in the example of FIGS. 24 to 28. In thiscase, the casing rotates in the reverse direction from the input shaft.

It will also be seen that the number of transmission members isgenerally equal to the number of tracks of the secondary cam increasedby one.

In the embodiment shown in FIGS. 36 to 41, the input shaft 1 carries aprimary cam 2 with two tracks. The intermediate element or output shaft3 comprises a plate 4 provided with projections 5 defining eight guides6 for the transmission members 13, which are eight in number. The casing7 has an internal peripheral surface forming the secondary cam which hassix tracks. The casing 7 being maintained fixed, the output shaft 3turns four times less quickly than the input shaft 1, which correspondsto the number eight, divided by the number of tracks of the primary cam,two. The two shafts 1 and 3 turn in the same direction.

In the embodiment shown in FIGS. 42 to 47, the shaft 1 is provided witha secondary cam 2 with four tracks disposed symmetrically about thisaxis. The intermediate element is constituted by a housing 80 pivoted onthe input shaft 1 on opposite sides of the secondary cam 2. This housing80 has five holes 81 provided in its peripheral wall, uniformly spacedabout the axis of this housing 80 and constituting recesses or guidesfor the transmission members constituted by the spherical balls 82.

The primary cam is in this instance formed by a ring 83 pivoted on thehousing 80 and of which the internal surface 84, which is eccentric,constitutes the primary cam which in this case has a single track.

If the intermediate element 80 is maintained stationary, one completerevolution of the ring 83 in a clockwise direction gives rise to therotation of ¼ of a turn in the reverse direction, of the shaft 1. Thereis thus precisely achieved a demultiplication ratio of 1 to 4, namely,in this case, equal to the number of tracks of the secondary cam dividedby the number of tracks of the primary cam. The number of transmissionmembers 82 is equal to the number of tracks of the secondary camincreased by the number of tracks of the primary cam, namely five. Ifthe input shaft 1 provided with the four tracks of the secondary cam 2is maintained fixed, the intermediate element 80 will turn five timesless rapidly than the primary cam 83 but in the same direction. Theratio will accordingly be 1 to 5.

In all the embodiments of the mechanism, the transmission members arealways permanently in contact with the primary and secondary cams andwith the intermediate element in which they slide radially.

This mechanism, which therefore has no play, permits a perfectdesmodromic transmission of the movement of one element on another.There is a continuous sliding or rolling of the transmission memberswhich have a perfectly smooth contact surface, circular or spherical, onthe primary cam and simultaneously on the secondary cam. It should benoted that this arrangement of the cams permits providing coaxial speedreducers whose housing turns more rapidly than the central shaft, whichis the reverse of all known existing systems.

The form of the transmissions can vary. They generally have, however, aspherical or cylindrical peripheral portion of circular cross-sectionwhich is in contact with each of the primary and secondary cams.

It will be noted that in all the embodiments described up to now, thetransmission members slide radially and perpendicularly relative to theaxis of the mechanism.

The embodiment of the desmodromic mechanism described with respect toFIGS. 51 to 54 operates again according to the same principle but thisembodiment is original and is particularly suitable for reducers ofsmall diameter having high demultiplication ratios.

This mechanism is inscribed within a tube or tubular envelope 90 closedat its two ends by flanges 91 giving passage to an input shaft 92 andrespectively an output shaft 93.

In this embodiment, the primary and secondary cams are no longerdisposed one within the other but axially in alignment one behind theother within the tubular envelope 90. This arrangement permits providingseveral stages of reduction one after the other and obtaining with threestages for example a reduction of 1 to 1000 and this in a diameter lessthan 8 mm and a length less than 25 mm.

The input shaft 92 is secured to a cylindrical element 94 pivoted in theenvelope 90 having on its front surface a surface 95 constituting theprimary cam comprising a track.

A tubular partition 96 positions a fixed secondary cam 97 constituted byan annular bell cam comprising four tracks. A first intermediate element98 is pivoted coaxially on the envelope 90. This intermediate element 98passes through the central opening of the bell cam 97 and has a hubgrooved in the direction of the primary cam 95. This hub comprises fivethroats or grooves 99 in which are disposed five balls 100 constitutingthe transmission members. The axial position of the secondary cam 97 andof this intermediate element 98, defined by the tubular partition 90,are such that when one ball 100 is in contact with the top of the trackof the primary cam 95, this ball will be in contact with the secondarycam 97 in the deeper one of its tracks.

FIGS. 53 and 54 show schematically the primary cam 95 and secondary cam97 as well as the five balls 100 in a linear development in twodifferent positions of the mechanism.

The demultiplication ratio of such a stage is equal to the number oftracks of the secondary cam increased by the number of tracks of theprimary cam, divided by the number of tracks of the primary cam, in thiscase (4+1):1=5; or according to the formula: secondary cam 360°:4=90°;transmission members 360°:5=72°; 90°−72°=18°; 90°:18°=5.

The free front surface of the intermediate element 98 itself also has aprimary cam 95 a acting on the balls 100 a sliding axially in a secondintermediate element 98 a and coacting with the four tracks of thesecond secondary cam 97 thereby forming a second demultiplication stageidentical to the first.

A third demultiplication stage of the mechanism is constituted by athird primary cam 95 b disposed on the front surface of the secondintermediate element acting on the balls 100 b sliding axially in a hub101 of the output shaft and coacting with the tracks of a thirdsecondary cam 97 b.

In this embodiment, the primary and secondary cams are coaxial andfacing, the secondary cams 97 are fixed, whilst the primary cams 95 turnabout the axis of the assembly and of the input shaft 92 and outputshaft 93.

In a modification, it is evident that the number of tracks of thesecondary cams 97, 97 a, 97 b of the different stage of demultiplicationcan be different, the number of grooves 99 of the intermediate element98 and of the transmission members 100 varying as a result. Thus, a verylarge choice of ratios, always whole numbers, is available.

It will also be noted here that the tangents to the points of contact ofat least two balls 100 with the primary cam 95 and secondary cam 97 formangles β, γ extending in opposite directions, preventing any movement ofthe mechanism when it is stopped.

The embodiment of the mechanism according to the invention shown inFIGS. 55 to 57 constitutes a jack or a linear mechanical actuator, againbased on the same principle of actuation and of demultiplication.

This mechanism comprises a fixed body 110 forming an intermediateelement on which is journalled a ring 111 whose eccentric internalsurface 112 constitutes the primary cam and one track of the mechanism.A linear actuating rod 113, cylindrical or polygonal, slides in the body110 and comprises at its end portion disposed in the body, at least onehourglass-shaped portion 114 constituting the secondary cam.

Holes 114, four in the illustrated example, pass through the bodyradially. These holes are angularly offset by 90° from each other andaxially by a distance equal to ¼ of the length L of the secondary cam114 of hourglass shape. The arrangement of these holes 115 relative tothe secondary cam 114 is such that the latter comprises by analogy threetracks.

Transmission members constituted by spherical balls 116 are slidablymounted in the holes 115 and are in permanent contact with the body 110and each of the primary cam 112 and secondary cam 114.

For one complete revolution of the ring 112 and hence of the primarycam, there is obtained a linear displacement of the actuating rod 113 ofa length L of the secondary cam of hourglass shape.

There are in this embodiment acute angles β and γ between the tangentsto the points of contact of two balls 116 with the primary cam 112 andsecondary cam 114, ensuring blocking of the mechanism when it isstopped.

FIG. 57 shows the mechanism when the ring 111 has carried out ¼ of aturn from the position shown in FIG. 54. The two balls have advancedrelative to the rod 113 by a quarter of the length of thehourglass-shaped cam.

This embodiment of the mechanism is particularly interesting because theactuating rod 113 can, independently of its linear movements controlledby the ring 111, carry out movements of rotation about itself withoutchanging its axial position.

The final embodiment of the mechanism, shown in FIGS. 58 to 62A, is alsoa linear displacement mechanism. It comprises a frame 120 constitutingthe intermediate element, in this case H-shaped in longitudinalcross-section. In the upper portion of the frame, between the legs ofthe H, is journalled an input shaft 121 secured to the primary cam, herecomprised by four eccentrics 122 a, b, c, d angularly offset by 90°relative to each other and representing the track of the primary cam.The horizontal bar of the H of frame 120 comprises four holes 123 eachaligned with one of the eccentrics 122 a, b, c, d, constituting theguides for the balls 124 comprising the transmission members.

In the lower portion of the frame 120 is provided a space in whichslides longitudinally, parallel to the axis of the input shaft 121, aportion of,a rod or bar 125 that is displaceable linearly on the rollers126. The upper surface of this bar 125 facing the holes 123 of the frame120 has a secondary cam 127 formed by successive hollows whichconstitute the tracks of this secondary cam. The distance Dcorresponding to the length of three successive tracks is equal to fourtimes the interaxial distance of the holes 123.

The smooth balls 124 are permanently in contact each with one of theeccentrics 122 a, b, c, d of the primary cam and with the secondary camand bear on the frame 120. This assembly corresponds to a mechanismcomprising one primary cam with one track and one secondary cam withthree tracks.

For one complete revolution of the input shaft 121 and hence of theprimary cam 122, there is obtained a linear movement of the bar equal to⅓ of the distance D, namely equal to the extent of one track of thesecondary cam.

In this embodiment also, the tangents to the point of contact of twoballs 124 with the primary cam 122 and secondary cam 125 form oppositeacute angles β and γ such that the elements 120, 121 and 125 of themechanism are blocked when the input shaft 121 is not driven inrotation.

In modifications, the transmission members can comprise a cylindricalbody and rounded ends. This transmission members can also be formed bythe juxtaposition of several rotating elements to limit friction.

In all of the embodiments of the mechanism, the primary cam is the oneof the two cams which has the fewer tracks. In all embodiments of themechanism, except the one shown in FIGS. 52 to 54, the guide axles ofthe rectilinear guides of the intermediate element are disposed radiallyand/or perpendicularly to the axis of the mechanism.

In the embodiment shown in FIGS. 52 to 54, by contrast, the guide axlesof the guides of the intermediate element are disposed parallel to theaxis of the mechanism.

In embodiments of the mechanism not shown, it can be provided that thetransmission members are connected to the intermediate element or to thebody of this intermediate element by other means than the rectilinearguides in which they slide. Thus, each transmission member can beconnected to the body of the intermediate element by a rod articulatedon the body of the intermediate element and carrying the transmissionmember. In such an arrangement, there is no friction but only rolling ofthe transmission members on the primary and secondary cams and on thebody of the intermediate element. In such an arrangement, the movementof the transmission members relative to the body of the intermediateelement takes place along an arc of a circle, namely, along ancurvilinear and nonrectilinear path.

What is claimed is:
 1. A desmodromic mechanism comprising: pluralmovement transmission members, each having axial ends, said transmissionmembers being connected to and bearing on an intermediate element; aprimary cam in permanent contact with each of said transmission members;a secondary cam in permanent contact with each of said transmissionmembers, wherein said transmission members have contact surfaces thatare shaped to ensure permanent and simultaneous contact with saidprimary and secondary cams, said primary cam, said secondary cam andsaid intermediate element being assembled with each other so as to moverotatably and/or linearly relative to each other and with invariabledifferential speeds for all positions of the desmodromic mechanism, saidintermediate element having rectilinear guides, said guides having guideaxles, said transmission members freely sliding in said guides; a spacebeing formed between two adjacent one of said transmission members, aportion of a body of said intermediate element being between said twoadjacent transmission members, and a portion of said secondary cam beingbetween said two adjacent transmission members; and two bearing surfacesin contact with said axial ends of said transmission members and saidportion of said body and said portion of said secondary cam defining asealed variable volume chamber as a function of a relative position ofsaid primary and secondary cams and of said intermediate element.
 2. Themechanism according to claim 1, wherein said variable volume chamber hasa first volume comprising passages between said intermediate element,two adjacent ones of said transmission members, said primary cam andsaid secondary cam, and a second volume bounded by front surfaces ofsaid transmission members and bearing surfaces of said transmissionmembers.
 3. The mechanism according to claim 2, wherein said primary camhas fluid distributing openings selectively placed about a periphery ofsaid primary cam.
 4. The mechanism according to claim 3, wherein atleast one of said openings disposed on the periphery of said primary camis in simultaneous communication with two adjacent variable volumechambers.
 5. The mechanism according to claim 1, wherein said secondarycam has fluid distributing openings selectively placed about a peripheryof said primary cam.
 6. The mechanism according to claim 1, wherein saidguide axles are disposed radially and/or perpendicularly to an axis ofthe desmodromic mechanism.
 7. The mechanism according to claim 1,wherein said transmission members are provided with a resilientlydeformable bandage.
 8. A desmodromic mechanism comprising: pluralmovement transmission members having a known number of transmissionmembers connected to and bearing on an intermediate element; a primarycam in permanent contact with each of said transmission members; asecondary cam in permanent contact with each of said transmissionmembers, wherein said transmission members have contact surfaces shapedto ensure permanent and simultaneous contact with said primary andsecondary cams, said primary cam, said secondary cam and saidintermediate element being assembled with each other so as to moverotatably and/or linearly relative to each other and with invariabledifferential speeds for all the positions of the desmodromic mechanism;a body forming said intermediate element, said primary cam comprising aring pivoted about said body, said ring having an internal eccentricsurface, said secondary cam and a rod being movable axially in saidbody; a portion of said rod located within said body, said secondary camhaving at least one region having an hourglass shape due to the rodbeing within said body, said body having rectilinear guides having guideaxles, said guides being uniformly distributed about a periphery of saidbody, said guides being offset axially from each other, and saidtransmission members moving radially in said guides perpendicular to theaxis of the desmodromic mechanism, said transmission members beingpermanently in contact with said primary cam and with said secondary camas well as with said intermediate element.
 9. The mechanism according toclaim 8, wherein said guides have an axial offset equal to a length ofthe hourglass-shaped region of said secondary cam divided by said numberof said transmission members.
 10. The mechanism according to claim 8,wherein said intermediate element has a frame supporting an input shaft,and said primary cam has a track having several eccentrics angularlyoffset relative to each other, each of said eccentrics having a sameamplitude and a same offset axially along said input shaft, said framehaving openings aligned with said eccentrics; and further comprising abar being mounted linearly displaceably relative to said frame, parallelto the input shaft, said bar having a surface facing said openings, saidsurface having successive hollows forming said secondary cam; and saidtransmission members sliding in said openings and permanently contactingwith one of said eccentrics and said secondary cam and bear on saidframe.
 11. The mechanism according to claim 10, wherein a distance Dcorresponding to a length of a number of successive recesses of saidsecondary cam, said number of successive recesses being equal to saidnumber of said transmission members less one, is equal to an interaxialdistance between two of said eccentrics of said primary cam multipliedby the number of said transmission members.
 12. The mechanism, accordingto claim 8, wherein said guide axles are disposed radially orperpendicularly to an axis of the desmodromic mechanism.
 13. Themechanism according to claim 8, wherein said transmission members areprovided with a resiliently deformable bandage.